A View of Earth

Luc Ikelle2012

A View of Earth (Apollo 17)

Dry lands (deserts)

Wetter climate

oceans

Antarctica: Glacial ice Ocean and atmosphere

Earth’s spheres (1) The most dynamic portion of Earth

– Atmosphere• Thin gaseous envelope surrounding Earth

– Hydrosphere• Water dominated by the oceans

– Biosphere• All living things on the planet

– Lithosphere• Rocky outer shell

Earth’s spheres: the atmosphere (2)

Composition is unique in the solar system–Provides Air we breathe and protects from

the Sun’s intense heat.–Thin (90% in 16 km) and tenuous–78% nitrogen–21% oxygen (not present in early atmosphere)–Minor amounts of carbon dioxide, argon

and water vapor

Earth’s spheres: the hydrosphere (3)

Total mass of water on or near Earth’s surface–Covers 71% of Earth’s surface–~98% in oceans–2% in glaciers, groundwater, lakes and

streams (fresh water)

(blue planet)

Earth’s spheres: the biosphere (4)

All life on Earth–Animals & plants on land, in the sea and

air (tree roots, flying insects and birds, …)–There life in ocean floor the pressure

is extreme and no light penetrate.–Microorganisms - the most common form

of life–Evolved within narrow zone near the

Earth’s surface

A view of Earth

• Earth’s spheres

• Earth’s interior: description

• Earth’s interior: evidence

• Major features of Earth’s surface

Earth’s internal structure

• Solid Earth has a layered structure–Layers defined by composition and physical

properties–Compositional layers

• crust - mantle - core

–Physical layers• lithosphere - asthenosphere - mesosphere - outer

core - inner core

Compositional Layers

Crust–Outermost compositional layer–Definite change in composition at the base

of the crust–2 types:

• Continental crust (up 75 km thick in Himalaya), • Oceanic crust (~ 8 km thick)

Compositional Layers

Mantle–Largest layer in the earth

• 2900 km thick• 82% by volume• 68% by mass

–Composed of silicate rocks with abundant iron and magnesium• Density ranges from 3.2 to 5 g/cc

Compositional Layers

Core–Central mass about 7000 km in diameter–Average density of 10.8 g/cc–16% by volume, 32% of mass– Indirect evidence of composition

• Metallic iron

Lithosphere/asthenosphere

Lithosphere mantle

Asthenosphere

Oceanic crust

Continental crust

Lithosphere

Lithosphere = crust + uppermost part of the mantleAstenosphere = part of the mantle beneath the lithosphere

The uppermost part of the mantle is strong and solidly attached to crust).

Physical layers:lithosphere

–Crust + upper portion of the mantle–Solid & rigid–Thickness ranges from 10 km beneath

oceans to 300 km in continental areas

Physical layers:continental crust

• Thick - up to 75 km• Lower density - 2.7 g/cm3

• Strongly deformed• Much older - may be billions of years old

Physical layers:oceanic crust

• Thinner - about 8 km• More dense - 3.0 g/cm3

• Comparatively undeformed• Much younger < 200 million years old

A view of Earth

• Earth’s spheres

• Earth’s interior: description

• Earth’s interior: evidence

• Major features of Earth’s surface

Waves

• Elastic waves are generated whenever there is– a sudden deformation– a sudden movement of a portion of the medium

Waves

• Examples of man-made seismic sources– Explosion– Weight drop– Drilling– Vibroseis (tractions), ...

Two types of deformations• Volumetric change

(P-waves, compressional waves)

• Change of shape

(S-wave, shear waves)

Source: Duan (2010)

P-waves (compressional waves)• P-waves (i) similar to sound waves, (ii) series of

contractions and relaxations, (iii) fastest, ~5 km/sec (depends on rock type), (iv) travel through solid, liquid and gas

Source: Ikelle and Amundsen (2005); IPS

S-waves (shear waves)• S-waves motion is (i) right angles to direction of wave, (ii) about

half the speed of P waves, and (iii) travel only through solids

Source: Ikelle and Amundsen (2005); IPS

P-wave

S-wave

Source: Duan (2010)

Horizontal source2.5 km

1.5

km

Source: petroleum-seismology.com

Sea surface (marine/offshore)(Air/water/solid)

2.5 km

1.5

km

Source: petroleum-seismology.com

Free surface (land/onshore)(Air/solid/solid)

2.5 km

1.5

km

Source: petroleum-seismology.com

Exploring Earth’s interior with seismic waves

• Seismic waves travel at different speeds in different rocks

Seismic waves & ground shaking • Surface waves: propagate near the Earth surface, slower than

body waves L-waves: Love, move back/forth (snake) R-waves: Rayleigh, move like ripples on a pond

Source: Duan (2010)

Source: Duan (2010)

Recording seismic waves: seismograms

• Seismograms: records of ground shaking• Waves arrive in sequence.

–P waves first–S waves second–Surface waves last (cause most of the property

damage in an earthquake).

Source: Duan (2010)

Interior with seismic waves • Discovery of Core-Mantle boundary: P-waves do not

arrive in the P-wave shadow zone (103° – 143°)

Source: Duan (2010)

Interior with Seismic Waves (cont.)• Discovering two parts of the core: liquid outer

core & solid inner core S-waves do not arrive in the S-wave shadow zone P-wave reflection within the core

Source: Duan (2010)

Source: Duan (2010)

refractionSource: Duan (2010)

A View of Earth

• Earth’s spheres

• Earth’s interior: description

• Earth’s interior: evidence

• Major features of Earth’s surface

World map

World map

World map

North and Central Americas

Central America

Caribbean sea

South America

Europe

Africa

Asia

Oceania

Pacific OceanAtlantic Ocean

Indian Ocean

Arctic Ocean

All oceans and seas together = the “world ocean”

Northern Hemisphere

Southern Hemisphere

• 61% ocean

• 81% ocean

BUT, on a planetary scale, the ocean is small

• 0.13% of Earth’s volume

• more water within Earth’s interior than in its ocean and atmosphere

Equator

http://www.uwsp.edu/geO/faculty/ritter/geog101/textbook/images/maps/oceans_CIA_base.jpg

Some Additional Statistics

Average land elevation = 840 m

Average ocean depth = 3,800 m

Average ocean temperature = 3.9oC

About 50% of Earth’s population lives <240 km from the ocean

• In Japan, 96% of the population lives <100 km from the ocean

Kola Superdeep Borehole (KSDB)

• A scientific drilling project in the USSR to drill into the Earth's crust

• goal = 15 km

• began digging in 1970

• in 1992, reached a final depth of 12 km • 245oC!

<1/500 of Earth’s radius

Problems• How do we know that the outer core is liquid?• Is the core a constituent of the asthenosphere?• List and briefly describe the four “spheres” that constitute

our environment.• Can P-wave velocity be greater than S-wave velocity?• Can S-wave propagate in the sea water?• Is Guatemala in North, Central, or South America?• Where is the Gulf of Aden?• Which one of these components (crust, mantle, core) of

Earth is the heaviest?• Which one of these components (crust, mantle, core)

occupies the largest volume of Earth.• Which one of these components (oceans and continents)

occupies the largest portion of the surface Earth.